In flat panel display of prior art, thin film transistor liquid crystal displays (TFT-LCDs) are dominant due to characteristics of low radiation, thin thickness and low power consumption, etc. and are widely used for various applications. Generally, when a user views the liquid crystal display from different viewing angles, the brightness of image may reduce as the viewing angle increases, resulting in limitation of viewing angle. In order to realize display with wide viewing angle, both in-plane switch (IPS) type liquid crystal display panel and fringe field switching (FFS) type liquid crystal display panel have been developed.
FIG. 1 is a partial plan view of a conventional FFS type liquid crystal display panel, with a color filter substrate therein omitted for the sake of clarity. FIG. 2 is a partially sectional view along A-A line in FIG. 1, with a black matrix layer and a color filter layer disposed on the color filter substrate omitted for the sake of clarity. With reference to FIGS. 1 and 2, the conventional FFS type liquid crystal display panel comprises a thin film transistor array substrate 100, a color filter substrate 200 and a liquid crystal layer 300 sandwiched between the thin film transistor array substrate 100 and the color filter substrate 200. The thin film transistor array substrate 100 comprises a transparent substrate 10, and a plurality of scanning lines 101 and data lines 102 formed on the transparent substrate 10, with the plurality of scanning lines 101 and data lines 102 crosswise defining a plurality of pixel regions. Each pixel region comprises a first transparent electrode 11 located on a lower layer and a second transparent electrode 14 located on an upper layer, the second transparent electrode 14 being provided as strips. The first transparent electrode 11 is a common electrode 11, and the second transparent electrode 14 is a pixel electrode 14. Each pixel region further comprises a thin film transistor 103 for controlling the pixel electrode 14. The pixel electrode 14 comprises a plurality of strip-like slots 140 and a plurality of strip-like pixel electrode portions 142 formed by means of the plurality of strip-like slots 140 and electrically connected to one another. There is a gate insulation layer 12 and a passivation layer 13 isolated between the pixel electrode 14 and the common electrode 11. A gate electrode of the thin film transistor 103 is a portion of the corresponding scanning line 101 or is electrically connected with the corresponding scanning line 101, a source electrode of the thin film transistor 103 is electrically connected with the corresponding data line 102, and a drain electrode of the thin film transistor 103 is electrically connected with the pixel electrode 14 via a through hole C located on the passivation layer 13.
In order to decrease driving voltage of the FFS type LCD panel and increase response speed of liquid crystal molecules, the liquid crystal layer 300 in the FFS type LCD panel often employs anisotropic liquid crystal molecules with positive dielectric constant, however, there is a drawback of low transmittance in the conventional FFS type LCD panel.
The FFS type LCD panel uses the strip-like pixel electrode portion 142 of the pixel electrode 14 located on the upper layer and the common electrode 11 located on the lower layer to form a fringe electric field, with the horizontal component of the fringe electric field being highest at the edge of the strip-like pixel electrode portion 142. In addition, it is possible for the liquid crystal molecules at the edge of the strip-like pixel electrode portion 142 to rotate in the plane parallel to the transparent substrate 10 since the anisotropic liquid crystal molecules with positive dielectric constant are prone to rotate in a direction parallel to the electric field under the action of the electric field. The liquid crystal molecules in the region between the strip-like pixel electrode portions 142 are under a slightly weaker vertical component but a higher horizontal component of the electric field than the liquid crystal molecules in the region above the strip-like pixel electrode portions 142. Moreover, the elastic force from rotation of liquid crystal molecules also drives the liquid crystal molecules to rotate in the plane parallel to the transparent substrate 10. Consequently, there is also a relatively high transmittance in the region of the FFS type liquid crystal display panel between the strip-like pixel electrode portions 142. However, the electric field has a relatively high vertical component above the strip-like pixel electrode portions 142, but the horizontal components of the electric field applied are almost counteracted, and therefore, the liquid crystal molecules above the strip-like pixel electrode portions 142 hardly rotate in the plane parallel to the transparent substrate 10, but only rotate in the plane perpendicular to the transparent substrate 10, that is, stand up inclinedly, resulting in lower transmittance right above the strip-like pixel electrode portion 142 of the pixel electrode 14.
FIG. 3 is a simulation effect view of transmittance of the FFS type LCD panel shown in FIG. 2. As shown in FIG. 3, the region right above the strip-like pixel electrode portion 142 of the pixel electrode 14 is under a relatively weak horizontal component of electric field, and the liquid crystal molecules, under the action of the relatively weak horizontal component of electric field, have relatively small twist angle, resulting in lower transmittance in these regions, and thus having an influence on the increase of transmittance of the whole FFS type LCD panel.
In the case that the first transparent electrode 11 located on the lower layer is a pixel electrode and the second transparent electrode 14 located on the upper layer is a common electrode, there is still a problem of lower transmittance corresponding to the region right above the second transparent electrode 14.